Cortrosyn for ACTH Stimulation in Dogs

By now most veterinarians in Toronto are aware that there are no commercially available ACTH products for veterinary use. Although frustrating at first it afforded me the opportunity to reevaluate the ACTH stimulation test on all fronts.

The ACTH stimulation test assesses adrenocortical reserve. Currently, I feel that the ACTH has serves three purposes:

1. It is the gold standard for the diagnosis of iatrogenic Hyperadrenocorticism (HAC).

2. It is the gold standard for the diagnosis of Hypoadrenocorticism (Addison’s disease).

3. It is the primary test for monitoring response during treatment of HAC.

The ACTH stimulation test is NOT an appropriate screening test for HAC as the sensitivity has been reported to be as low as 57%.

• In other words if the patient’s test is within the normal range that doesn’t rule out HAC.

As well it does not differentiate between Pituitary-dependent (PD) HAC and Adrenal-dependent (AT) HAC. The low-dose dexamethasone suppression test should be used as the screening test for HAC as it has better sensitivity and may be useful to distinguish between the two forms: PDH and ADH. However, dogs with an abnormal LDDST should also have an adrenal ultrasound to further localize the disease.

ACTH Gel/Compounded ACTH

Studies have investigated the use of compounded ACTH. Potential variability between pharmacies and between bottles exist. Matrin, L. et al. investigated the use of compounded ACTH in normal dogs and found that the cortisol concentrations at 60 mins were similar to Cortrosyn, but at later times varied considerably. The protocol for using compounded ACTH is as follows:

• Dose is 2.2 U/kg IM

• Collect blood samples prior to and 1 hr and 2 hrs after administration of ACTH

Cortrosyn

Synacthen and Cortrosyn are the products of choice for performing an ACTH stimulation but currently Cortrosyn is the only available commercial ACTH product. Cortrosyn can be obtained from your purchasing group. Cortrosyn is supplied in vials containing 0.25 mg (250 μg) of synthetic ACTH (cosyntropin). Each bottle is expensive.

The current protocol is as follows:

• Administer 5 μg/kg up to a maximum of 250 μg

• Administer IV

• Collect blood samples prior to and 1 hr after administration of ACTH

As Cortrosyn is expensive and the dose required for maximal stimulation of the adrenal glands for small to medium sized dogs is small, each vial can be diluted and stored for up to six months. This can help make it a more cost effective process for you and your clients.

Procedure to Dilute and Store Cortrosyn

1. Each vial of Cortrosyn contains a power that is reconstituted by adding 2.5 ml of sterile saline resulting in a concentration of 100 μg/ml

2. Once reconstituted, divide into either 5 doses of 50-μg (0.5 ml) or 10 doses of 25-μg (0.25 ml). The doses should be drawn up into plastic tuberculin syringes

3. DO NOT store reconstituted Cortrosyn in glass containers or vials

4. Label the syringes with the product, dose in each syringe, and the date it was reconstituted

5. Freeze each of the syringes at -20C and try to avoid storing these syringes in a frost-free freezer

If you have any questions regarding Cortrosyn or ACTH stimulation tests please do not hesitate to contact Dr. Michael Goldstein, Dr. Stephen Kruth or Dr. Kim Ho at 416-784-4444 or by email at ctvrc@live.ca